Individuals at risk for Huntington’s disease (HD) have the option of undergoing genetic testing, which detects the presence or absence of the genetic sequence that causes HD. The decision of whether or not to undergo genetic testing is intensely personal, with many factors to consider. This chapter will provide scientific background information regarding genetic testing for Huntington’s disease.

Let’s start with the basics of genetics. The word “genome” refers to an organism’s complete set of DNA. The fundamental building block of our genome is the molecule known as DNA. You’ve no doubt heard of DNA many times before – in the news, in movies, on television. Yet in order to understand Huntington’s disease, it is important to gain a good understanding of DNA and how DNA is related to genes. Our goal in this section is to review the basic features of the structure and function of the main molecule of heredity.

What causes the onset of HD? Current research shows that there is an abundance of information to be learned regarding the genetic origins of HD. Let’s trace HD’s beginnings from the molecular level, exploring the relationships between a gene, a protein, aggregation “clumps,” neural cell death, and the disease itself.

In order to make predictions about the future spread or decline of Huntington’s Disease, we can draw upon scientific tools from the field of population genetics (see Part I for an introduction to this field).

With their sword-wielding, karate-chopping, and pizza-eating ways, the Teenage Mutant Ninja Turtles swept American children by storm in the early 1990s. Unfortunately, though they did get kids to sit still for 30 minutes each day, the turtles also contributed to a widely held public misconception about what it means to have a mutation. From watching their television program, one might think that people with mutations will grow green skin and begin a new life in the city’s sewer pipes. In reality, though, there is nothing out of the ordinary about mutations. In fact, every person in the entire world has some sort of mutation in his or her DNA; in that sense, everyone is a mutant! Mutations are not just normal, they are important: evolution itself cannot occur without mutations.

Have you ever wondered where Huntington’s disease originated? Or why it’s predominantly found among Europeans and those of European descent? Population genetics, the study of the genetic makeup of populations and of changes over time in that makeup, attempts to answer such questions. In this chapter, we explore the origins of the HD allele, the variable frequency of HD around the world, and current theories for how the HD allele has “survived” through time in human populations.

Proteins and what they do

Proteins are very important molecules to all forms of life. They are one of four of life’s basic building blocks; the other three are carbohydrates (sugars), lipids (fats), and nucleic acids (DNA and RNA).